1. Field of the Invention
The present invention relates to a flotation process for separating solids from a paper stock-containing suspension may be introduced to a flotation tank through an inlet opening and a clarified accepted stock, e.g., a fibrous suspension free of foreign matter or clarified (or pure) water, may be conveyed out through an outlet opening. Due to the flotation process, at least a part of the solids present in the suspension may be concentrated in a foam collected on a surface and may be removed from the flotation tank. At least a predominant part of the suspension flowing into the flotation tank may be routed through a guiding element so that, before entry into the guiding element, the flowing suspension may aspirate a portion of the suspension already present in the flotation tank. Accordingly, the guiding of the flows occurs through the guiding element at a speed less than approximately 2 m/sec.
The present invention may also relate to a mixing device for carrying out the above-noted flotation process. The mixing device may include a mixing element having at least one inlet opening for introducing the paper stock-containing suspension into the flotation tank. Further, the mixing device may include at least one guiding element having at least one influx opening located downstream of the inlet opening and spaced a predetermined distance from the inlet opening. A collecting chamber may be positioned within the predetermined distance between the inlet opening and the influx opening.
2. Discussion of Background Information
Processes of the kind generally disclosed above have been discussed, e.g., in German patent publication 34 01 161. These processes are used in the paper industry for removal of printing inks, glues, or other interfering impurities during the processing of recycled paper. Due to their hydrophobic properties, the fibers in the suspension are removed as accepted stock, while the impurity solids are discarded with the foam. Because of this separation of solids into fibers and impurities, this process has been called selective flotation. Other uses for the general flotation process discussed above is in the removal of as large as possible a percentage of solids from a liquid suspension, e.g., in treatment of waste water produced by pressing in the paper industry. This process has been called clarifying flotation or, because of a gassing mechanism, decompression flotation.
As mentioned above, processes of this type have been in use for a long time and have a relatively high standard of effectiveness. Nevertheless, there is a demand for further improving the effectiveness of the flotation process.